Sensation and Perception 6-8% of AP ExamChapters 4 & 5

Pioneers in S & P

Ernst Weber 1795-1878Gustav Fechner 1801-1887

• Ernst Weber = Noted for defining:• Absolute Threshold = The minimum

stimulus that can be detected 50% of the time

• difference threshold (JND) aka Weber’s Law= the smallest difference between stimuli that we can detect

• Fechner = Studied brightness, light and afterimages by looking directly at the sun (Bad Idea!)• Used Weber’s law to study

relationship between physical magnitude of a stimulus & it’s perceived magnitude

Sensory Systems• Senses gather

info (sight, hearing, touch, taste, smell)

• detect incoming information

• Encode in neural activity

• Transfer info to brain

1. Accessory structure (ex: ears) takes in info “energy”

2. Transduction takes place in sensory receptors= turn info into neural activity

3. Sensory Nerves carry info to the spinal cord & brain

4. Info sent to thalamus to analyze info (switchboard)

5. Info sent to cerebral cortex = produces sensation & perception = voila!

The Eye & Optical Illusions

A closer look at the Vision• http://education-portal.co

m/academy/lesson/how-does-vision-work.html#lesson

Blue Man Group: Rods & Coneshttp://www.youtube.com/watch?v=W-yLfm5HsHc

Contrast Effects• Hermann Grid

• In addition to the pattern of black boxes, we see black dots in the intersections of the white lines.

• This phenomenon is called a contrast effect • due to the way in

which light contrasts are interpreted by our eyes

The red/pink lines are parallel in the image above.  However, they appear to bend or bulge outward due to the rays extending from the center.  This is known as the standard Herring illusion (dating to 1861).

Geometric Illusions

http://opticaleffect.tripod.com/hering_illusion1.htm

The concentric squares are, in fact, parallel, but the diagonal lines in the background make them appear slanted and crooked.  This illusion also exhibits some aspects of contrast effects, as the boxes around the edge seem to pop out.

In the Muller-Lyer illusion, both horizontal lines are the same length but the orientation of the "arrows" makes the bottom one seem longer than the top one.

Which line is longer?

in the Judd illusion the orientation of the "arrow" on each end causes the midpoint (as marked) to appear off-center. 

The first (left) one appears to bulge out and the second (right) one seems to ripple like a flag or waves, when in fact both are normal checkerboards.

  In the images above there are three partial shapes (either circles or squares).  They are oriented, however, such that their cut out portions appear to frame another shape (either a square or a triangle). 

Illusions of Structure and Form

We immediately recognize this as an elephant and at first see nothing wrong with it...only to realize that something indeed is quite wrong!  The Gestalt laws of "good form" come to bear here: we know an elephant and recognize it pre-consciously without analyzing the image of it.

Look at the cube below and pay particular attention to the brown cell in the middle of each side. How do they compare? Do they all look like the same shade of brown??

Now look at the "masked" version of the same image below, in which the neighboring cells are darkened and ignored by the visual system. Notice: the brown cells are the same color.

Here is another similar example in which the dotted central tile is actually the same color:

As with the cube, this is because the neighboring colored tile influence our perception of the color of the center tile: it is seen as "bluer and lighter" next to reds and brown and is seen as "browner" next to "greener" greens and more blue (right).   In other words, the nearby tiles weight the ratio of cone responses and therefore different colors are perceived! 

If you take a look at the following  picture , it looks animated…it’s not!  Your eyes are making it move.  To test this, stare at one spot for a couple seconds and everything will stop moving.  Or look at the black center of each circle and it will stop moving.  But move your eyes to the next black center and the previous will move after you take your eyes away from it....   

Which circle in the middle is bigger?

You should see a man's face and also a word...Hint: Try tilting your head to the right, the world begins with 'L'

Color Deficiencies

• See photos on page 132 of book• Previously called color blindness = Cones contain only 2 of the

3 possible color sensitive pigments

Skin Senses• Body’s largest sense receptor system• Receptors for this system are located throughout the body

Two point threshold activity• Skin’s Function =

• Keeps us in• Receives info from the world

• Goal = Measure the difference between the stimulus –is it felt as one poke or as two separate ones? Where? How far apart?

• Alternate roles of subject & experimenter• Step 1 = experimenter hold ends of toothpicks about 1 cm

apart. Touch the subject (gently!) on various areas (ex: cheek, nose, hand, palm of hand, fingertips, parts of arm, neck, leg, calf).

• Step 2 = subject will state whether they feel one toothpick or two. This tests the JND threshold)

• Switch roles and repeat experiment

Gate Control Theory (Melzak) • Sensation of pain requires

not only that pain information from skin receptors be active, but also the neural gate in the spinal cord to allow these signals to pass to the brain (the gate is closed when critical fibers in the spinal cord are activated)

• Pressure stimulation tends to close the neural gate (activate the critical fibers) which is why rubbing a hurt area may relieve pain temporarily.

The Chemical Senses: Taste and Smell

Olfaction = detects airborne chemicalsOlfaction = detects airborne chemicalsGustation = detects chemicals through Gustation = detects chemicals through

receptors in mouthreceptors in mouth

http://education-portal.com/academy/lesson/taste-touch-and-smell.html#lesson

Gustation

• Taste cells are chemical sensitive receptors located in taste bud clusters

• Taste buds are located on the bumps on your tongue

Basic qualities of taste:

SweetSourSaltyBitter

UmamiOther influences may be smell,

temperature or “touch”/texture

Sensory Interactionthe principle that one sense may influence anotheras when the smell of food influences its taste

Olfaction• Receptors for smell are located on the olfactory patch which is

a thin membrane in the upper nasal cavity• Olfactory cells are stimulated by gases dissolved in the fluid

covering the membrane• For stimulus to be “smelled,” it must be dissolved

Audition

Audition the sense of hearing

Frequency the number of complete wavelengths that

pass a point in a given timePitch

a tone’s highness or lowness depends on frequency

http://education-portal.com/academy/lesson/mechanics-of-hearing.html#lesson

Backmasking:• http://jeffmilner.com/backmasking/• Mental set = predisposition to perceive something• Listen w/o subtitles • Listen with subtitles = “perceptual set”

• brain is focused on relating the sounds with the words • Brain expects the words to match the sounds

The Intensity of Some Common Sounds

Audition

Deafness- May be caused bytumors, skull injury, poison, birth trauma, rubella

Conduction Hearing Loss hearing loss caused by damage to the mechanical system that

conducts sound waves to the cochlea Nerve Hearing Loss

hearing loss caused by damage to the cochlea’s receptor cells or to the auditory nerve

Vestibular Sense• Equilibratory sense• Knowledge of body position as in sense of balance• Receptors in semicircle canals (rotating movement) and

vestibular sacs (straight line movement) in inner ear

Senses• Optical Illusions TED talk• https://www.ted.com/talks/

beau_lotto_optical_illusions_show_how_we_see

• Synesthesia TED talk• http://ed.ted.com/lessons/what-color-is-tuesday-exploring-

synesthesia-richard-e-cytowic